Waste plastic disposal apparatus

ABSTRACT

A waste plastic disposal apparatus (K1-K4) including a storage portion (2) for storing waste plastic; a heating portion (7) for heating the waste plastic, which includes a heater (7b) and a fan (7a); a hot-air circulating path (20) for circulating hot air therethrough, which is defined by the storage portion (2) and the heating portion (7); an exhaust path (10) which branches off from the hot-air circulating path (20); and a deodorizing portion (9) which is provided in the exhaust path in response to intake of a predetermined quantity of external air into the hot-air circulating path (20) per unit time, the hot air in the hot-air circulating path (20) is exhausted in a quantity equal to the predetermined quantity from the exhaust path (10) through the deodorizing portion (9).

TECHNICAL FIELD

The present invention relates to a waste plastic disposal apparatus forreducing the volume of plastic waste such as plastic wrapping materials,plastic packing materials, plastic containers or the like produced insmall-scale firms, stores, etc.

BACKGROUND ART

Plastic is widely used for one-way applications for food wrappingmaterials, containers, packing materials, etc. but is actually discardedas refuse in a large quantity. Thus, in Japan, a law on recycling ofwrapping and containers was recently enacted from a standpoint ofreduction of quantity of refuse, saving of energy and saving ofresources and obligates recycling of such plastic. In order to promoterecycling of plastic, not only legal regulation but economic approach isvital. As one trial, it is proposed to lower the cost of recycledplastic through reduction of transportation and collection costs byreducing volume of plastic with a mechanical crushing and cuttingmachine, a mechanical compressive apparatus, a mechanical crushing andfrictional heat dissolving apparatus, etc. However, these prior artapparatuses have large disposal capacities but are large and expensiveand therefore, are not suitable for use in terminal collection spotssuch as supermarkets where a relatively small quantity of plastic isdisposed of.

On the other hand, a method suitable for disposal of a relatively smallquantity of plastic, in which plastic is heated at low temperatures soas to be reduced in volume, is proposed in Japanese Patent Laid-OpenPublication No. 5-23655 or Japanese Patent Laid-Open Publication No.5-92179. This method simplifies structure of the apparatuses as comparedwith conventional ones and is suitable for a compact apparatus fordistributed disposal of a small quantity. However, in this known method,since plastic is heated so as to be reduced in volume, malodorous gasmay be produced according to the kinds of plastic or heating temperatureduring the heating process and thus, malodor may be produced from theapparatus during and after disposal. Especially, in case where thedisposal apparatus is used in stores such as supermarkets, production ofmalodorous gas could offer a serious problem. Furthermore, in this knownmethod, in case plastic has been heated at an excessively hightemperature due to malfunction of control of the apparatus orcombustible volatiles such as kerosine are mixed into the apparatus,there is a risk in that a large quantity of combustible gas is producedand reaches its ignition point.

Therefore, in conventional disposal of waste plastic, there have beensuch problems that technology for removing malodor quickly andeffectively should be established and ignition of produced gas should beprevented under any condition.

SUMMARY OF THE INVENTION

The present invention has for its object to provide, with a view toeliminating the above described disadvantages of conventional wasteplastic disposal apparatuses, a compact and inexpensive waste plasticdisposal apparatus in which production of malodor at the time of heatingof waste plastic is prevented, production of combustible gas duringimproper operation is restrained and ignition of produced gas isprevented and which is suitable for small-scale firms, stores andhousehold.

In order to accomplish this object, a waste plastic disposal apparatusof the present invention comprises: a storage portion for storing wasteplastic, which includes a lid; a heating portion for heating the wasteplastic, which includes a heater and a fan; a hot-air circulating pathfor circulating hot air therethrough, which is defined by the storageportion and the heating portion; an exhaust path which branches off fromthe hot-air circulating path; and a deodorizing portion which isprovided in the exhaust path; wherein in response to intake of apredetermined quantity of external air into the hot-air circulating pathper unit time, the hot air in the hot-air circulating path is exhaustedin a quantity equal to the predetermined quantity from the exhaust paththrough the deodorizing portion.

It is desirable that the external air in a volume not less than 20% of avolume of the hot-air circulating path is carried into the hot-aircirculating path per minute.

In accordance with the present invention, since quantity of gas producedat the time of heating of waste plastic is reduced, the produced gas isdeodorized and risk of ignition of the produced gas is obviated, such aremarkable effect is gained that volume of waste plastic can be reducedsafely and effectively at small-scale firms, etc.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a fragmentary longitudinal sectional view of a waste plasticdisposal apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a fragmentary longitudinal sectional view of a catalyticdeodorizing portion of the waste plastic disposal apparatus of FIG. 1.

FIG. 3 is a fragmentary longitudinal sectional view of a catalyticdeodorizing portion of a waste plastic disposal apparatus according to asecond embodiment of the present invention.

FIG. 4 is a fragmentary longitudinal sectional view of a waste plasticdisposal apparatus according to a third embodiment of the presentinvention.

FIG. 5 is a fragmentary longitudinal sectional view of a waste plasticdisposal apparatus according to a fourth embodiment of the presentinvention.

FIG. 6 is a front elevational view of an anti-flaming portion of thewaste plastic disposal apparatus of FIG. 5.

FIG. 7 is a sectional view taken along the line VII--VII in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention are described withreference to the drawings.

(First embodiment)

FIG. 1 shows a waste plastic disposal apparatus K1 according to a firstembodiment of the present invention. The waste plastic disposalapparatus K1 includes an apparatus housing 1 and a storage portion 2 forstoring waste plastic. The storage portion 2 includes a storagecontainer 2a for storing waste plastic and a lid 2b provided at an upperportion of the storage container 2a. A vertically movable bottom plate 3is provided in the storage container 2a so as to press waste plastic,while a stretchable and hermetic bag 4 is provided under the bottomplate 3 and is coupled with an air pump 5. Meanwhile, a heat insulatingvessel 6 is provided between the apparatus housing 1 and the storagecontainer 2a.

The waste plastic disposal apparatus K1 further includes a heatingportion 7 for heating waste plastic. The heating portion 7 isconstituted by a pressure sirocco type fan 7a, a heater 7b, a hot-airinlet 7c provided at an upper portion of a side wall of the storagecontainer 2a and a suction port 7d for sucking hot air, which isprovided at a lower portion of the heating insulating vessel 6.

In addition, the waste plastic disposal apparatus K1 includes atemperature sensor 8 for detecting temperature of hot air blown from thehot-air inlet 7c into the storage container 2a, a catalytic deodorizingportion 9, a hot-air circulating path 20 for circulating hot air, whichis defined by the storage portion 2 and the heating portion 7, anexhaust path 10 which branches off from the hot-air circulating path 20and leads to the catalytic deodorizing portion 9 and an external airintake 11 provided at a suction port of the fan 7a.

As shown in FIG. 2, the catalytic deodorizing portion 9 includes acatalytic portion 9a in which platinum series oxidizing catalyst iscarried by honeycomb ceramic, a heater 9b provided upstream of thecatalytic portion 9a and a temperature measuring portion 9c formeasuring temperature of the catalytic portion 9a.

Hereinafter, operation of the waste plastic disposal apparatus K1 of theabove described arrangement is described. Initially, the lid 2b isopened and waste plastic is put into the storage container 2a so as tobe placed on the bottom plate 3. Subsequently, by turning on the fan 7aand the heater 7b, hot air is blown from the hot-air inlet 7c to thewaste plastic in the storage container 2a. At this time, temperature ofhot air is measured by the temperature sensor 8 and is controlled so asto be not less than a glass transition temperature (plastic softeningtemperature) and not more than a plastic fusion temperature. As shown bythe arrow A in FIG. 1, hot air blown from the hot-air inlet 7c into thestorage container 2a proceeds into the heat insulating vessel 6 fromhot-air outlets 15 provided on the storage container 2a and then, issucked to the suction port 7d by the fan 7a so as to be circulated. Atthis time, external air is drawn from the external air intake 11 havingnegative pressure due to wind pressure of the fan 7a and ventilates thehot-air circulating path 20.

Meanwhile, by utilizing pressure of the fan 7a, hot air in the wasteplastic disposal apparatus K1 is carried, in a quantity corresponding toan intake quantity of external air, to the catalytic deodorizing portion9 via the exhaust path 10 and then, is exhausted. At this time, thecatalytic portion 9a is arranged to be heated by the heater 9b to apreset temperature of the temperature measuring portion 9c. Finally,after the waste plastic has been heated, the bag 4 is expanded byfeeding air into the bag 4 by the air pump 5 so as to lift the bottomplate 3. As a result, the waste plastic is compressed between the bottomplate 3 and the lid 2b so as to be subjected to plastic deformation.

The waste plastic disposal apparatus K1 aims chiefly to reduce volume ofgeneral-purpose waste plastic by heating and compressing it. To thisend, when waste plastic is heated, temperature of hot air is controlled,while being detected by the temperature sensor 8, so as to range from alower limit set at the glass transition temperature at which elasticityof plastic drops sharply to an upper limit set at the plastic fusiontemperature for restraining fusion of plastic. Thus, it is possible tocompress the waste plastic by small stress. However, plastic may emitmalodorous gas during its heating according to kinds of plastic, therebyresulting in possible exhalation of malodor from the waste plasticdisposal apparatus K1. Therefore, in this embodiment, not only externalair in a volume not less than 20% of a volume of the hot-air circulatingpath 20 is carried into the hot-air circulating path 20 per minute buthot air in a volume equal to the above mentioned volume of external airis deodorized through oxidative destruction by the catalytic deodorizingportion 9 so as to be exhausted such that the waste plastic disposalapparatus K1 is ventilated. As a result, quantity of gas produced duringheating of waste plastic can be reduced effectively.

Meanwhile, in this embodiment, on the basis of plastic which produces alarge quantity of gas, 20% of the volume of the hot-air circulating path20 is set at a minimum ventilation quantity of external air carried intothe hot-air circulating path 20 per minute. It is needless to say thateffectiveness of reducing produced gas is enhanced in proportion toventilation quantity. In case only plastic which produces less gas isdisposed of, ventilation quantity is not required to be large but may bedetermined in view of capacity and economic aspect of the catalyticdeodorizing portion 9. Meanwhile, in this embodiment, the fan 7a of theheating portion 7 is used for intake of external air into the hot-aircirculating path 20 and feed of hot air to the catalytic deodorizingportion 9. However, two fans therefor may also be provided separately.Furthermore, pneumatic pressure is used for a compressive mechanism forcompressing waste plastic but similar compressive effect can be gainedby any compressive mechanism for applying stress to waste plastic, forexample, a rack-and-pinion mechanism, a mechanism for applying load fromabove, etc. Meanwhile, plastic having large thermal shrinkage, forexample, foamed polystyrene can be considerably reduced in volume onlyby providing a heating mechanism without providing the compressivemechanism referred to above.

Hereinafter, a first example of the first embodiment is described inwhich foamed polystyrene exhaling malodor at the time of its heating isdisposed of as waste plastic by the waste plastic disposal apparatus K1.When heated, foamed polystyrene emits a large quantity of malodorousgases such as styrene acting as residual monomer, toluene acting asfoaming auxiliary, etc. Furthermore, at this time, a large quantity ofsuch residual components of foaming agent as butane, pentane,cyclohexane, etc. are also produced. The quantity of gas produced fromfoamed polystyrene is apt to be larger as the time period after foamingis shorter. Immediately after foaming of a foamed polystyrene, foamingagent resides in a quantity of 2 to 3% by weight of foamed polystyrene.Therefore, if a large quantity of foamed polystyrene is heated withoutventilation immediately after foaming, concentration of gas produced inthe storage container 2a may fall within its combustible range.Therefore, also from a standpoint of safety, ventilation quantity of thewaste plastic disposal apparatus K1 should be set to a large value.Thus, in this example, ventilation quantity is set at 60 l/min. on thebasis of a volume of about 150 l of the hot-air circulating path 20 anda disposal capacity of about 600 g/operating cycle for foamedpolystyrene by the waste plastic disposal apparatus K1. Meanwhile,generally, quantity of produced gas is inclined to increase inproportion to heating temperature. Therefore, in order to prevent suddenproduction of gas from foamed polystyrene by distributing temperature offoamed polystyrene, heating conditions in which the temperature of hotair is raised gently from 110° C. to 130° C. and finally reaches 150° C.at the hot-air inlet 7c are employed. As a result, at the ventilationquantity of 60 l/min., production of malodor can be prevented and gasproduced by heating foamed polystyrene can be reduced to a safeconcentration. Meanwhile, in this example, it was confirmed that when aventilation quantity of 30 l (corresponding to 20% of the volume of thehot-air circulating path 20)/min. or more is employed, gas produced byheating foamed polystyrene can be reduced to a safe concentration. Atthis time, ventilation quantity was adjusted by changing area of theexternal air intake 11. Meanwhile, by heating foamed polystyrene by hotair of 150° C., its volume is reduced to about 1/30 of its originalvolume.

Then, a second example of the first embodiment is described in which PETbottles emitting less gas are disposed of as waste plastic by the wasteplastic disposal apparatus K1. Gas is scarcely produced from PETbottles. However, by heating PET bottles, malodor is exhaled fromresidues of the PET bottles. However, in this example, it was confirmedthat when not only external air in a volume not less than 20% of thevolume of the hot-air circulating path 20 is carried into the hot-aircirculating path 20 per minute but hot air in a volume equal to theabove mentioned volume of external air is deodorized through oxidativedestruction by the catalytic deodorizing portion 9 so as to beexhausted, produced malodor is destroyed substantially. Meanwhile, byheating and compressing the PET bottles simultaneously, its volume isreduced to about 1/12 of its original volume.

Hereinafter, a third example of the first embodiment is described inwhich volume of waste plastic is reduced by setting cross-sectional areaof the exhaust path 10 so as to set flow velocity of exhaust of hot airat not less than 1 m/sec. on the basis of exhaust quantity of hot airfrom the hot-air circulating path 20. In this concrete example, heatingcontrol is performed such that an upstream face of the catalytic portion9a usually assumes 500° C. As a result, if volatile combustiblecomponents penetrate into the catalytic deodorizing portion 9 or a largequantity of combustible gas is produced from waste plastic, such a riskmay arise that the catalytic deodorizing portion 9 acts as an ignitionsource for igniting such gases. Meanwhile, generally, maximum combustionspeed of combustible hydrocarbon components at ordinary temperature isless than 1 m/sec. Therefore, in this example, in order to avoid theabove mentioned risk, the cross-sectional area of the exhaust path 10 isset so as to set flow velocity of exhaust of hot air at not less than 1m/sec. on the basis of exhaust quantity of hot air delivered to thecatalytic deodorizing portion 9. By setting the flow velocity of exhaustof hot air delivered to the catalytic deodorizing portion 9 at not lessthan 1 m/sec. ignition of gas in the waste plastic disposal apparatus K1by the catalytic deodorizing portion 9 can be prevented alsotheoretically.

Then, tests were made in order to investigate whether or not back fireoccurs due to the catalytic deodorizing portion 9 acting as an ignitionsource. In the tests, butane gas and styrene gas which are produced byheating foamed polystyrene are put in the waste plastic disposalapparatus K1 at an approximately identical concentration and then, it isexamined whether or not these gases are ignited by the catalyticdeodorizing portion 9. The tests have revealed that when flow velocityof exhaust of hot air is not less than 1 m/sec., back fire of butane gasand styrene gas from the catalytic deodorizing portion 9 does not occur.

(Second embodiment)

FIG. 3 shows a catalytic deodorizing portion 19 of a waste plasticdisposal apparatus K2 according to a second embodiment of the presentinvention. The catalytic deodorizing portion 19 is structurally similarto the catalytic deodorizing portion 9 of the waste plastic disposalapparatus K1 except that a temperature measuring portion 9d formeasuring temperature of exhaust air is provided at an exhaust port.Since other constructions of the waste plastic disposal apparatus K2 aresimilar to those of the waste plastic disposal apparatus K1, thedescription is abbreviated for the sake of brevity.

In the waste plastic disposal apparatus K2 of the above describedarrangement, the catalytic portion 9a is preheated to a presettemperature prior to the start of heating of waste plastic and thetemperature of exhaust air is measured by the temperature measuringportion 9d during preheating of the catalytic portion 9a such thatdisposal of waste plastic is controlled on the basis of the temperatureof exhaust air.

In order to reduce quantity of gas produced by heating waste plastic inthe waste plastic disposal apparatus K2, a ventilation arrangementsimilar to that of the waste plastic disposal apparatus K1 is employedin which external air is carried into the waste plastic disposalapparatus K2 and hot air in the waste plastic disposal apparatus K2 isexhausted through the catalytic deodorizing portion 19. Ventilationquantity and quantity of reduction of produced gas have correlation.Thus, in order to sufficiently reduce the quantity of produced gas, itis necessary to secure a predetermined ventilation quantity. However, ifthe capacity of the fan 7a drops or clogging of the exhaust path 10occurs, ventilation quantity may decrease. Therefore, in thisembodiment, ventilation quantity to the catalytic deodorizing portion 19is estimated from temperature measured by the temperature measuringportion 9d at the time temperature measured by the temperature measuringportion 9c has reached a preset value during preheating of the catalyticportion 9a for the following reason. Namely, ventilation quantity andquantity of heat carried from an upstream side to a downstream side ofthe catalytic portion 9a per unit time are correlated to each other.Therefore, ventilation quantity of hot air to the catalytic deodorizingportion 19 can be estimated from temperature measured by the temperaturemeasuring portion 9d at the time temperature measured by the temperaturemeasuring portion 9c has reached the preset value during preheating ofthe catalytic portion 9a. By performing disposal after it has beenconfirmed by these operations that not less than the predeterminedventilation quantity is obtained, malodor can be reduced positively.

Hereinafter, a first example of the second embodiment is described inwhich ventilation quantity of hot air to the catalytic deodorizingportion 19 is estimated by using the waste plastic disposal apparatusK2. In this concrete example, exhaust temperature of hot air is measuredwhen ventilation flow rate of hot air to the catalytic deodorizingportion 19 is set at 0, 30, 45 and 60 l/min. and the catalytic portion9a is preheated such that temperature measured by the temperaturemeasuring portion 9c assumes 400° C. Meanwhile, temperature of externalair is 20° C. When ventilation flow rate is 0, 30, 45, 60 l/min., theexhaust temperature of hot air at the time temperature measured by thetemperature measuring portion 9c has reached 400° C. assumes 21, 65, 167and 273° C., respectively. Thus, it was found that exhaust temperaturerises in response to increase of ventilation flow rate. In order to setminimum exhaust quantity at not less than 30 l/min. based on thesemeasurement results in this example, temperature measured by thetemperature measuring portion 9d at the time temperature measured by thetemperature measuring portion 9c has reached the preset value is set at100° C.

Meanwhile, by detecting ventilation flow rate at the time of start ofdisposal of waste plastic, it is possible to detect clogging of theexhaust path 10 or failure of the fan 7a. Meanwhile, if control in whichtransfer to a heating process of waste plastic does not take place isperformed in case exhaust flow rate is small, production of a largequantity of gas can be prevented preliminarily when foamed polystyreneleading to production of a large quantity of gas is disposed of.Furthermore, even if volatile combustible components such as kerosineare erroneously introduced into the waste plastic disposal apparatus K2,disposal can be prevented in advance and thus, there is no risk that thecombustible components in the waste plastic disposal apparatus K2 areignited during a preheating process. At this time, since volatilizedcombustible components are delivered to the catalytic deodorizingportion 19 together with hot air and are oxidized by the catalyticdeodorizing portion 19 so as to produce heat, exhaust temperature at thetime of preheating exhibits a value higher than that at the time ofproper preheating. Therefore, by setting an upper limit of exhausttemperature, it is possible to detect penetration of combustiblecomponents into the waste plastic disposal apparatus K2. Meanwhile,exhaust temperature during preheating varies according to size of thewaste plastic disposal apparatus K2, disposal conditions, etc. andtherefore, should be, needless to say, set in accordance with thesefactors.

Meanwhile, plastic may exhale malodor from its heating temperatureaccording to its kinds. Therefore, in case heating of the catalyticportion 9a is started concurrently with heating of waste plastic in thewaste plastic disposal apparatus K2, there is a possibility that malodorleaks because the catalytic portion 9a is not heated sufficiently. Inorder to cause the catalytic deodorizing portion 19 employing platinumseries oxidizing catalyst to function effectively, the catalytic portion9a should be heated to its activation. Thus, in this embodiment,activity of the catalyst is promoted by preheating the catalytic portion9a so as to deal with also malodor produced at an initial stage ofheating of waste plastic. Hereinafter, a second example of the secondembodiment is described in which foamed polystyrene is disposed of, asplastic exhaling malodor at low temperatures, by using the waste plasticdisposal apparatus K2. Foamed polystyrene emits styrene when heated to atemperature of about 80° C. Therefore, in case disposal is startedwithout preheating the catalytic portion 9a, malodor of styrene can beconsiderably perceived from the catalytic deodorizing portion 19 at aninitial stage of heating of foamed polystyrene. However, it wasconfirmed that when heating of foamed polystyrene is started after thecatalytic portion 9a has been preheated to 400° C., malodor of styreneis scarcely perceived from the catalytic deodorizing portion 19 at aninitial stage of heating of foamed polystyrene. Meanwhile, in thisexample, the catalytic portion 9a is preheated to 400° C. at whichstyrene can react fully. However, it is desirable that this preheatingcondition should be set in consideration of the kinds of plastic to beheated, produced gas and its catalytic reactivity.

In the second embodiment, upper limits may be, respectively, allotted totemperature measured by the temperature measuring portion 9c andtemperature measured by the temperature measuring portion 9d such thatheating of the catalytic portion 9a and waste plastic is controlled whentemperature measured by the temperature measuring portion 9c andtemperature measured by the temperature measuring portion 9d exceed therespective upper limits. In case foamed polystyrene producing a largequantity of gas is disposed of by the waste plastic disposal apparatusK2, a large quantity of styrene acting as residual monomer, malodorousgas such as toluene acting as foaming auxiliary and residual componentsof foaming agent such as butane, pentane, cyclohexane, etc. are producedas described in the first embodiment. If these components are deliveredto the catalytic deodorizing portion 19 at high concentrations, quantityof heat produced at the catalytic portion 9a increases and thus,temperature of the catalytic portion 9a may exceed its heat-resistanttemperature. Therefore, the upper limit is allotted to temperaturemeasured by the temperature measuring portion 9c. If temperaturemeasured by the temperature measuring portion 9c exceeds the upperlimit, electric power inputted to the heater 9b for heating thecatalytic portion 9a is reduced such that excessive heating of thecatalytic portion 9a by the heater 9b is prevented. Furthermore, inorder to reduce the quantity of gas produced from foamed polystyrene,control for reducing electric power inputted to the heater 7b forheating waste plastic is performed.

Meanwhile, since foaming agent contained in foamed styrene variesaccording to use applications and makers, the composition of producedgases is not fixed. For example, if much butane gas having catalyticreactivity inferior to that of other gases is present, much reaction ofbutane gas takes place at a downstream side of the catalytic portion 9aand thus, temperature measured by the temperature measuring portion 9cdisposed upstream of the catalytic portion 9a does not rise so much. Asa result, if the heater 9b for heating the catalytic portion 9a iscontrolled only by the temperature measuring portion 9c, temperaturedownstream of the catalytic portion 9a may exceed the heat-resistanttemperature of the catalytic portion 9a. Hence, also in the case wheretemperature measured by the temperature measuring portion 9d disposeddownstream of the catalytic portion 9a, exceeds the upper limit, controlfor reducing electric power inputted to the heater 9b for heating thecatalytic portion 9a and the heater 7b for heating waste plastic isperformed. By using these controls by the temperature measuring portions9c and 9d in combination, not only excessive heating of the catalyticportion 9a can be prevented but quantity of gas produced from wasteplastic can be reduced.

Hereinafter, a third example of the second embodiment is described inwhich heating of the catalytic portion and foamed polystyrene iscontrolled on the basis of the upper limit of temperature measured bythe temperature measuring portion 9c and the upper limit of temperaturemeasured by the temperature measuring portion 9d as described above. Inthis example, an upper limit of 500° C. and an upper limit of 600° C.are, respectively, allotted for temperature measured by the temperaturemeasuring portion 9c and temperature measured by the temperaturemeasuring portion 9d and control for reducing electric power inputted tothe heater 9b for heating the catalytic portion 9a and the heater 7b forheating waste plastic is performed on the basis of these upper limits.When a large quantity of gas has been produced from foamed polystyrene,temperature measured by the temperature measuring portion 9c andtemperature measured by the temperature measuring portion 9d exceed therespective upper limits. However, at this time, since electric powerinputted to the heater 7b is reduced, heating of foamed polystyrene iscontrolled such that quantity of gas produced from foamed polystyrene isreduced. It was confirmed that by simultaneously lowering electric powerinputted to the heater 9b, excessive heating of the catalytic portion 9acan be prevented.

Meanwhile, in the above example, the upper limits are, respectively,allotted for temperature measured by the temperature measuring portion9c and temperature measured by the temperature measuring portion 9d.However, an upper limit may also be allotted for only one of temperaturemeasured by the temperature measuring portion 9c and temperaturemeasured by the temperature measuring portion 9d in the case of disposalof waste plastic producing a small quantity of gas and in accordancewith purpose of disposal such that heating of the catalytic portion 9aand waste plastic is controlled. Namely, in case an upper limit isallotted for only temperature measured by the temperature measuringportion 9c, control for lowering electric power inputted to the heaters9b and 7b is performed when temperature measured by the temperaturemeasuring portion 9c exceeds the upper limit. Likewise, in case an upperlimit is allotted for only temperature measured by the temperaturemeasuring portion 9d, control for lowering electric power inputted tothe heaters 9b and 7b is performed when temperature measured by thetemperature measuring portion 9d exceeds the upper limit.

Furthermore, in the case where a large quantity of combustible gas hasbeen produced due to excessive heating of waste plastic or erroneousintroduction of combustible components into the waste plastic disposalapparatus K2, heat resistance of the catalytic portion 9a may present aproblem and combustible components may reach a concentration sufficientfor ignition. Therefore, in the third example of the second embodiment,a maximum upper limit of 800° C. may be allotted for both temperaturemeasured by the temperature measuring portion 9c and temperaturemeasured by the temperature measuring portion 9d. At this time, in casetemperature measured by the temperature measuring portion 9c hasexceeded the upper limit of 500° C. and in case temperature measured bythe temperature measuring portion 9d has exceeded the upper limit of600° C., control for lowering electric power inputted to the heaters 9band 7b is performed. On the other hand, in the case where temperaturemeasured by the temperature measuring portion 9c has exceeded themaximum upper limit of 800° C. and in the case where temperaturemeasured by the temperature measuring portion 9d has exceeded themaximum upper limit of 800° C., heating of the catalytic portion 9a andwaste plastic is stopped. Under this control, if volatile combustiblecomponents penetrate into the waste plastic disposal apparatus K2,temperature measured by the temperature measuring portion 9c andtemperature measured by the temperature measuring portion 9d exceed themaximum upper limit of 800° C., so that heating of the catalytic portion9a and waste plastic is stopped and thus, disposal of waste plastic canbe stopped positively. Namely, by performing control for stoppingdisposal of waste plastic in the case where at least on of thetemperatures measured by the temperature measuring portion 9c and thetemperature measuring portion 9d has exceeded the maximum upper limit of800° C., such effects can be gained in that the risk of ignition ofproduced gas upon entry of foreign matter is lessened and excessiveheating of the catalytic portion 9a is prevented.

Meanwhile, in the above example, the upper limit and the maximum upperlimit are allotted for each of the temperatures measured by thetemperature measuring portion 9c and the temperature measuring portion9d. However, the upper limit and the maximum upper limit may also beallotted for only one of the temperature measuring portion 9c and thetemperature measuring portion 9d in the case of disposal of wasteplastic producing a small quantity of gas and in accordance with purposeof disposal such that heating of the catalytic portion 9a and wasteplastic is controlled. Namely, in the case where the upper limit and themaximum upper limit are allotted for only temperature measured by thetemperature measuring portion 9c, control for lowering electric powerinputted to the heaters 9b and 7b is performed when temperature measuredby the temperature measuring portion 9c has exceeded the upper limit. Onthe other hand, when temperature measured by the temperature measuringportion 9c has exceeded the maximum upper limit, heating of thecatalytic portion 9a and waste plastic is stopped. similarly, in casethe upper limit and the maximum upper limit are allotted for onlytemperature measured by the temperature measuring portion 9d, controlfor lowering electric power inputted to the heaters 9b and 7b isperformed when the temperature measured by the temperature measuringportion 9d has exceeded the upper limit. On the other hand, whentemperature measured by the temperature measuring portion 9d hasexceeded the maximum upper limit, heating of the catalytic portion 9aand waste plastic is stopped. It is desirable that the maximum upperlimit is set in accordance with heat-resistant temperature of catalystand ignition temperature of produced gas.

(Third embodiment)

FIG. 4 shows a waste plastic disposal apparatus K3 according to a thirdembodiment of the present invention. In the waste plastic disposalapparatus K3, a temperature sensor 12 is provided in the exhaust path 10leading to the catalytic deodorizing portion 9. Since otherconstructions of the waste plastic disposal apparatus K3 are similar tothose of the waste plastic disposal apparatus K1, the description isabbreviated for the sake of brevity.

The waste plastic disposal apparatus K3 is operated in the same manneras the waste plastic disposal apparatus K1 except that temperature ofhot air in the exhaust path 10 is measured by the temperature sensor 12during disposal of waste plastic and exhaust flow rate of hot air isdetected on the basis of changes of temperature of hot air such thatdisposal of waste plastic is controlled.

In order to reduce quantity of gas produced by heating waste plastic inthe waste plastic disposal apparatus K3, a ventilation arrangementsimilar to that of the waste plastic disposal apparatus K1 is employedin which external air is carried into the waste plastic disposalapparatus K3 and hot air in the waste plastic disposal apparatus K3 isexhausted through the catalytic deodorizing portion 19. To this end, itis desirable that not less than a predetermined ventilation quantity issecured during disposal of waste plastic. In the waste plastic disposalapparatus K2, it is possible to detect ventilation quantity at aninitial stage of disposal of waste plastic but it is difficult to detectventilation quantity during disposal of waste plastic.

Therefore, in this embodiment, by measuring changes of temperature ofhot air in the exhaust path 10 by the temperature sensor 12, ventilationquantity during disposal of waste plastic is detected. Usually, sincehot air in a predetermined quantity corresponding to ventilationquantity is delivered to the catalytic deodorizing portion 9,temperature of hot air in the exhaust path is substantially fixed. Onthe other hand, in a case where the ventilation quantity drops due toclogging of the external air intake 11 of the fan 7a, etc., quantity ofheat carried per unit time by hot air decreases but heat dissipation inthe exhaust path 10 does not diminish so much, so that temperature ofhot air in the exhaust path 10 drops. Therefore, by detecting changes oftemperature of hot air in the exhaust path 10 by the temperature sensor12 provided in the exhaust path 10, it is possible to judge a drop inthe state of exhaust flow rate of hot air. Consequently, it is possibleto detect ventilation quantity during disposal of waste plastic.

Hereinafter, one example of the third embodiment is described in whichventilation quantity is detected from changes of temperature of hot airin the exhaust path 10 by using the waste plastic disposal apparatus K3.In this example, temperature of external air is 20° C., exhaust flowrate of hot air to the catalytic deodorizing portion 9 is set at 0, 30and 60 l/min. and temperature of hot air in the hot-air circulating path20 is set at 130° C. At this time, when exhaust flow rate of hot air tothe catalytic deodorizing portion 9 is set at 0, 30 and 60 l/min.,temperature of hot air in the exhaust path 10, which is measured by thetemperature sensor 12, assumes 40, 80 and 120° C., respectively. Thus,temperature of hot air in the exhaust path 10 drops in response toreduction of exhaust flow rate of hot air. Therefore, by measuringchanges of temperature of hot air to the catalytic deodorizing portion 9during disposal of waste plastic, it is possible to detect exhaust flowrate of hot air. Based on this, the exhaust flow rate of 30 l/min. isset as a minimum ventilation quantity. Thus, in the case wheretemperature of hot air in the exhaust path 10, which is measured by thetemperature sensor 12, has dropped to not more than 80° C., control isperformed such that disposal of waste plastic is stopped immediately.

Meanwhile, changes of temperature of hot air in the exhaust path 10 inresponse to changes of ventilation quantity are greatly influenced byheat dissipation in the exhaust path 10. However, if temperature ofexternal air is measured preliminarily prior to disposal of wasteplastic and control based on the temperature is performed, it ispossible to positively detect changes of ventilation quantity.

In this embodiment, the temperature sensor 12 is provided in the exhaustpath 10. However, a pressure sensor may be provided in the exhaust path10 in place of the temperature sensor 12 such that ventilation quantityis detected by measuring changes of pressure of hot air in the exhaustpath 10 by the pressure sensor.

(Fourth embodiment)

FIG. 5 shows a waste plastic disposal apparatus K4 according to a fourthembodiment of the present invention. In the waste plastic disposalapparatus K4, an anti-flaming portion 13 including a metallic gauze 13ahaving a mesh of not more than 1 mm is provided in the exhaust path 10leading to the catalytic deodorizing portion 9. FIGS. 6 and 7 illustratean arrangement of the anti-flaming portion 13 in detail. Since otherconstructions of the waste plastic disposal apparatus K4 are similar tothose of the waste plastic disposal apparatus K1, the description isabbreviated for the sake of brevity.

In this embodiment, heating control of the catalytic deodorizing portion9 is performed such that an upstream face of the catalytic portion 9areaches 500° C. Therefore, in case volatile combustible componentspenetrate into the catalytic deodorizing portion 9 or a large quantityof combustible gas components are produced from waste plastic, there isa risk that the catalytic deodorizing portion 9 will act as an ignitionsource for igniting such gases. As described in the first embodiment,such risk can be obviated by setting the exhaust flow rate of hot air inthe exhaust path 10 at not less than 1 m/sec. However, exhaust flow rateof hot air may become less than 1 m/sec. due to failure of the fan 7a,etc. On the other hand, the minimum energy required for ignitingcombustible gaseous mixture depends on the geometrical shape of a heatsource. Thus, by providing a gap for disabling propagation of thisenergy, i.e., an anti-flaming distance, spreading of fire can beprevented. Therefore, in this embodiment, since the anti-flaming portion13 having the metallic gauze 13a is provided in the course of theexhaust path 10 leading to the catalytic deodorizing portion 9,spreading of fire from the catalytic deodorizing portion 9 is prevented.

Meanwhile, in the waste plastic disposal apparatus K4, since flammablecombustible components cannot be specified, an anti-flaming distance isroughly calculated on the basis of a minimum ignition energy of butanegas produced in the largest quantity from foamed polystyrene and themetallic gauze 13a having a mesh of not more than 1 mm is employed fromthis anti-flaming distance. However, it can be easily imagined that whenthe anti-flaming distance is roughly calculated from this minimumignition energy, spreading of fire can be fully prevented also for othercombustible components by the anti-flaming distance.

Hereinafter, one example of the fourth embodiment is described in whichanti-flaming effects of the anti-flaming portion 13 are investigated inthe waste plastic disposal apparatus K4. In this example, isobutane gasacting as foaming agent of foamed polystyrene is employed as combustiblegas. When isobutane gas fed from an upstream side of the anti-flamingportion 13 is ignited at a downstream side of the anti-flaming portion13, it is examined whether or not back flow of fire to the upstream sideof the anti-flaming portion 13 happens by changing mesh of the metallicgauze 13a. At this time, isobutane gas falls within its combustiblerange and exhaust flow velocity of hot air in the exhaust path 10 is setto be not more than a value corresponding to an exhaust flow rate of 60l/min. As a result, it was found that no fire spreads to the upstreamside of the anti-flaming portion 13 including the metallic gauze 13ahaving a mesh of not more than 1 mm. Furthermore, even if the hot-aircirculating path 20 is set to a gas concentration leading to ignition inthe catalytic deodorizing portion 9, no fire spreads across theanti-flaming portion 13.

Meanwhile, in this embodiment, the metallic gauze 13a having a mesh ofnot less than 1 mm is employed in the anti-flaming portion 13. However,also when any incombustible member formed with pores having a mesh ofnot more than 1 mm is employed in place of the metallic gauze 13a, thesame anti-flaming effects as the metallic gauze 13a can be achieved.

As will be clear from the foregoing description, in the waste plasticdisposal apparatus of the present invention, by heating waste plastic tonot less than the glass transition temperature so as to lower themechanical strength and then, compressing the waste plastic, the volumeof the waste plastic is reduced effectively. Meanwhile, during disposalof waste plastic, in response to intake per minute of external air in avolume not less than 20% of a volume of the hot-air circulating pathinto the hot-air circulating path defined by the storage portion and theheating portion, hot air in a volume equal to the above mentioned volumeof external air is exhausted from the hot-air circulating path throughthe deodorizing portion such that the waste plastic disposal apparatusis ventilated. As a result, quantity of gas produced by heating wasteplastic is reduced effectively.

Meanwhile, in the case where the catalytic deodorizing portion mainlyconsisting of oxidizing catalyst is used as the deodorizing portion,ventilation quantity can be estimated by measuring changes oftemperature of exhaust of hot air from the catalytic deodorizing portionin the process for preheating the catalytic deodorizing portion to thepreset temperature or by measuring changes of temperature of pressure ofhot air in the exhaust path during heating of waste plastic. Meanwhile,by controlling heating of the catalyst and waste plastic on the basis ofmeasurement results of temperature of exhaust air during disposal ofwaste plastic, excessive production of gas at the time of heating ofwaste plastic and excessive heating of the catalyst can be prevented.

Furthermore, when exhaust flow velocity of hot air in the exhaust pathleading to the deodorizing portion is set to be not less than 1 m/sec.or the anti-flaming portion including the metallic gauze having a meshof not more than 1 mm is provided in the exhaust path, spreading of firefrom the catalytic deodorizing portion to combustible components isprevented.

By disposal of waste plastic as described above, since volume of wasteplastic is reduced safely and effectively at small-scale firms, etc.where waste plastic is produced, efficiency for recovering waste plasticcan be raised and recycling of waste plastic can be performedeconomically.

We claim:
 1. A waste plastic disposal apparatus comprising:a storageportion for storing waste plastic, said storage portion including a lid;a heating assembly for heating the waste plastic in said storageportion, said heating assembly including a first heater and a fan,wherein said storage portion and said heating assembly define a hot-aircirculating path for circulating hot air; an exhaust conduitcommunicating with the hot-air circulating path; a deodorizing deviceconnected to said exhaust conduit for deodorizing gases exhaustedthrough said exhaust conduit, said deodorizing device comprising acatalytic portion, a second heater for heating said catalytic portion,and a first temperature measuring device, disposed downstream of saidsecond heater, for measuring the temperature of said catalytic portion,wherein said first temperature measuring device is operable to determinewhen the temperature of said catalytic portion exceeds a firstpredetermined upper limit temperature of said catalytic portion; a powersupply connected to said first and second heaters, wherein the powersupplied to said first and second heater is reduced when the firsttemperature measuring device measures a temperature of the catalyticportion, which exceeds a first predetermined upper temperature limit;and an external air intake communicating with said fan, wherein, inresponse to intake of a predetermined quantity of external air into thehot-air circulating path per unit time, a portion of the hot air in thehot-air circulating path is exhausted through said exhaust conduit andsaid deodorizing device in a quantity which is equal to thepredetermined quantity of external air.
 2. A waste plastic disposalapparatus as claimed in claim 1, wherein said catalytic portion includesan oxidizing catalyst.
 3. A waste plastic disposal apparatus as claimedin claim 1, wherein said fan of said heating assembly is operable tocreate a negative pressure such that external air is sucked into thehot-air circulating path.
 4. A waste plastic disposal apparatus asclaimed in claim 3, wherein the air sucked into the hot-air circulatingpath is at least 20% of the volume of the hot-air circulating path.
 5. Awaste plastic disposal apparatus as claimed in claim 1, wherein:saidfirst temperature measuring device is operable to measure a secondpredetermined upper temperature limit which is higher than the firstpredetermined upper temperature limit, said supply of power to saidfirst and second heaters is reduced when said first temperaturemeasuring device measures a temperature between the first and secondpredetermined upper limits, and said supply of power to said first andsecond heaters is cutoff when said first temperature measuring devicemeasures a temperature in excess of the second predetermined uppertemperature limit.
 6. A waste plastic disposal apparatus as claimed inclaim 1, wherein said deodorizing device further comprises a secondtemperature measuring device for measuring the temperature of theexhaust gas, said second temperature measuring device being disposeddownstream of said catalytic portion.
 7. A waste plastic disposalapparatus as claimed in claim 1, wherein a cross-sectional flow area ofsaid exhaust conduit is selected such that a flow velocity of the hotair exhausted through said exhaust conduit is greater than or equal to 1m/sec.
 8. A waste plastic disposal apparatus as claimed in claim 1,further comprising a temperature sensor disposed in said exhaust conduitfor measuring the temperature of the hot-air in said exhaust conduit,wherein a flow rate of hot-air through said exhaust conduit can beestimated from changes of the temperature of the hot-air measured by thetemperature sensor prior to and during disposal of the waste plastic,and, when the estimated flow rate of the hot-air has drops to less thanor equal to a preset value, heating of the waste plastic is terminated.9. A waste plastic disposal apparatus as claimed in claim 1, furthercomprising a pressure sensor disposed in said exhaust conduit formeasuring pressure in said exhaust conduit, wherein a flow rate ofhot-air in said exhaust conduit can be estimated from pressure changesof the hot air measured by the pressure sensor prior to and duringdisposal of the waste plastic, and, when the estimated flow rate of thehot air drops to less than or equal to a preset value, heating of thewaste plastic is terminated.
 10. A waste plastic disposal apparatus asclaimed in claim 1, further comprising an anti-flaming structureprovided in said exhaust conduit upstream of said deodorizing device,said anti-flaming structure including a metallic gauze having a mesh ofnot more than 1 mm.
 11. A waste plastic disposal apparatus as claimed inclaim 1, further comprising a compressing means for compressing thewaste plastic.
 12. A waste plastic disposal apparatus as claimed inclaim 11, wherein said compressing means comprises:a plate member whichmovable disposed in said storage portion; a stretchable bag provided inthe vicinity of said plate member; and an air pump connected to saidbag.
 13. A method of disposing of waste plastic comprising:supplyingwaste plastic in a storage portion; heating the waste plastic in thestorage portion by circulating hot air through a hot-air circulatingpath, wherein a first heater and a fan are provided in the hot-aircirculating path; exhausting a portion of the hot air through an exhaustconduit, wherein the exhaust conduit extends between the hot-aircirculating path and a catalytic deodorizing device which includes asecond heater and a catalytic portion; detecting a temperature of thecatalytic portion in the catalytic deodorizing device; reducing powersupplied to the first heater and the catalytic deodorizing device whenthe detected temperature exceeds a firs predetermined temperature; andstopping the supply of power to the first heater and the catalyticdeodorizing device when the detected temperature exceeds a secondpredetermined temperature, wherein the second predetermined temperatureis greater than the first predetermined temperature.
 14. A method ofdisposing of waste plastic as claimed in claim 13, further comprisingdeveloping a negative pressure with the fan such that air is suckedthrough an external air intake in communication with the fan such thatthe portion of hot air exhausted through the exhaust conduit and thecatalytic deodorizing device is equal to the quantity of external airsucked into the hot-air circulating path.
 15. A method of disposing ofwaste plastic as claimed in claim 13, further comprising detecting atemperature of the exhaust hot-air at location downstream of thecatalytic portion.
 16. A method of disposing of waste plastic as claimedin claim 13, further comprising:sensing a temperature in the exhaustconduit prior to and during disposal of the waste plastic; calculatingthe changes in temperature in order to estimate the rate of flow of theexhaust hot air through the exhaust conduit; and stopping heating of thewaste plastic when the estimated flow rate drops below a predeterminedvalue.